Topologies
36 SL500: Interface Reference Manual • July 2008 Revision: F • 96122
The 19 inch rack space within the libraries supports the installation of Fibre
Channel hubs or switches. This allows most of the fiber cabling to reside inside the
library enclosure.
Because of the fast growth and the increase in demand of Fibre Channel
attachments, hubs can provide cascading (multiple) loops within a fibre channel
network (see “Cascading Hubs” on page 37).
Considerations for Hubs
Jitter is a consideration when selecting, installing, and configuring hubs within a
Fibre Channel network. Jitter is the deviation of timing of an exchange.
The accumulation of jitter occurs and continues to grow within a chain of
repeaters. As a signal is input to a repeater, jitter is not removed from the clock and
is transferred to the data at the output. At some level within the network, jitter
could exceed the allowable limit causing excessive errors. Assuring that there are
N_Ports within the loop to reclock the signal, jitter will be minimized.
Loop Port State Machines (LPSM) are required to control the operation of the loop
and ensure Loop Initialization Protocol (LIP) is executed whenever a reset or
power-on occurs.
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